A content sharing system using mobile communication with mobile telephone terminals operated by batteries can reflect the operations from both terminals upon the same content stored in both of the mobile telephone terminals that are communicating with each other. More specifically, a chat service by using characters, a bulletin board service, a service with which photographs are mutually sent and shared, and a service with which hand-written characters and the like are written mutually, for example, can be achieved by the content sharing system.
With one-on-one communication or communication among a large number of users in particular with this type of services, it is required to increase the realtime property of the bidirectional operations via the mobile telephone terminals. For example, in a case where the same content shared between the terminals is a still image such as a photograph, the content sharing system transmits operations such as writing of hand-written characters, expansion/contraction, and the like executed on the image from one of the terminals to the other terminal in a real time manner as an incremental update command, and reflects the result of the operation on the same content stored in the other terminal. It is required to be able to perform the incremental update action in a realtime manner. In order to do that, it is necessary to establish and maintain a session (connection) between the both terminals or to perform regular polling with high frequency.
FIG. 19 is an explanatory chart showing the structure of an existing content sharing system 1001. The content sharing system 1001 is so structured that terminals 1020a, 1020b, a content sharing server 1010, and switching equipment 1040 can be connected to each other via a network 1002. The terminals 1020a and 1020b are more specifically mobile telephone terminals, smartphone terminals, personal computer terminals, and the like.
The terminals 1020a and 1020b can perform a voice call and data communication simultaneously via the network 1002, the content sharing server 1010 mediates the data communication between the terminals, and the switching equipment 1040 mediates the voice call between the terminals. The voice call may use the network 1020 same as the data communication or may use a different telephone network.
A content sharing application 1032 is operated in each of the terminals 1020a and 1020b. Further, a content 1031 as the same data is stored in both terminals. The content 1031 may be any data on which some kind of operations can be done with the terminals 1020a and 1020b, such as still images, videos, music, word-processed documents, spreadsheets, and the like.
When some kind of operation is executed by a user of one of the terminals 1020 and 1020b on the content 1031 via the content sharing application 1032, the content sharing application 1032 generates an incremental update command showing the content of the operation and transmits the incremental update command from one of the terminals to the other terminal via the content sharing server 1010. As a result, the content of the operation executed on the content 1031 in one of the terminals is reflected upon the content 1031 stored in the other terminal.
With the content sharing system 1001, it is possible to execute the above-described operations while exchanging voice conversations between the terminals 1020a and 1020b. The content sharing system 1001 is an example of a multimedia communication service in which the voice call and data communication are merged by using IMS (Internet protocol Multimedia Subsystem), and it can be applied to the use of video conferences, voice chats, and the like. Currently, the technical developments that can be utilized for such multimedia communication services are actively done.
As technical documents related to that, there are following techniques. Among those, depicted in Patent Document 1 is an SIP tunneling device which mutually switches the communication protocols between SIP (Session Initiation Protocol) and “own protocol”. Depicted in Patent Document 2 is a protocol switching device which switches data communicated with an application with HTTP (Hyper Text Transfer Protocol) to SIP according to “proper condition” of the type of the data and the like when a data acquiring unit relays the data.
Depicted in Patent Document 3 is an SIP application server and the like, which switch the protocol to be used based on the priority order determined in advance so as to be able to provide a service to a terminal that is not compatible with a specific communication method. Depicted in Patent Document 4 is a protocol switching device which switches communication data of SIP to be able to be used in a terminal device that employs HTTP. Depicted in Non-Patent Document 1 is the outline of an existing technique regarding IMS.    Patent Document 1: Japanese Unexamined Patent Publication 2002-247130    Patent Document 2: Japanese Unexamined Patent Publication 2010-050617    Patent Document 3: Japanese Unexamined Patent Publication 2010-056632    Patent Document 4: JP No. 4273899    Non-Patent Document 1: Nakazawa et. al., “Terminal Application Platform for Achieving IMS Service” OKI Technical Review No. 210, April, 2007 OKI Electric Industry Co., Ltd.
The communication protocols used in general in the content sharing system 1001 shown in FIG. 19 are mainly two kinds of protocols called HTTP (Hypertext Transfer Protocol) and SIP (Session Initiation Protocol). HTTP is the communication protocol used most frequently in transferring contents on websites on a network, and it is used in many cases also in the content sharing system. This is because the consumption of server resources (server resources such as remaining amount of a memory) of the content sharing server 1010 is small since it is unnecessary to establish a session (connection) between the terminals 1020a and 1020b which are communicating with each other.
However, with HTTP, data cannot be directly transmitted from the terminal 1020a as one of the terminals to the other terminal 1020b (push-type communication). Thus, each of the terminals 1020a and 1020b is required to connect to the content sharing server 1010 regularly to check if there is any communication directed for the terminal itself. This is called “polling”. Since it is necessary to perform polling regularly, each of the terminals 1020a and 1020b consumes the power constantly even when no data communication is being executed.
In the meantime, SIP is the communication protocol used frequently for video conferences, Internet telephones, and the like. With SIP, data can be transmitted directly from the terminals 1020a as one of the terminals to the other terminal 1020b by using the push-type communication such as MSRP (Message Session Relay Protocol), so that it is unnecessary to perform regular polling.
Therefore, the power consumption of each of the terminals 1020a and 1020b can be made smaller with the use of SIP than the case of using HTTP. Meanwhile, it is necessary to establish a session between each of the terminals 1020a and 1020b within the content sharing server 1010, so that a great amount of server resource is consumed.
It is by all means necessary to suppress the power consumption of each of the terminals 1020a and 1020b in the above-described content sharing system 1001 to be low and to suppress the consumption of the server resource of the content sharing server 1010 as much as possible so that a greater number of terminals can be participated in the communication. In that sense, SIP and HTTP are in a trade-off relationship with which it is difficult to achieve the both in terms of the power consumption of the terminals and the consumption of the server resource of the content sharing server.
However, Patent Documents 1 to 4 and Non-Patent Document 1 described above do not disclose a technique which makes it possible to reduce both the power consumption of the terminals and the consumption of the server resource in the content sharing server. The techniques depicted in Patent Documents 1 to 2 and Patent Document 4 are related to “change” of the protocol but not related to “switching” of protocols, so that it is not possible to suppress the power consumption and the consumption of the server resource by switching the communication protocols.
Patent Document 3 discloses “switching” of the protocols. However, this technique switches the protocols according to “priority” but does not switch the protocol according to the frequency of generating the incremental update command. Further, this technique does not suppress the power consumption.
The object of the present invention is to provide a content sharing system, a mobile terminal, a protocol switching method, and a program thereof, which are capable of reducing the power consumption in the terminals and to effectively utilize the server resource.